Difference Between Tropic and Nastic Movement

The key difference between tropic and nastic movement is that tropic movement is a directional response while nastic movement is a non-directional response.

Plants respond to different types of stimuli, such as light, water, gravity, touch, and chemicals. Some plant parts also show movements as a response to a stimulus. Some responses depend on the direction of the stimulus, but some responses do not. Based on this, there are two main types of plant movements as tropic movements and nastic movements. Tropic movements are the responses shown by plant parts depending on the direction of the stimulus, while nastic movements are the non-directional responses shown by plants without depending on the direction of the stimulus. Generally, tropic movements are slow movements, while nastic movements are fast movements.

CONTENTS

1. Overview and Key Difference
2. What is Tropic Movement
3. What is Nastic Movement
4. Similarities Between Tropic and Nastic Movement
5. Side by Side Comparison – Tropic vs Nastic Movement in Tabular Form
6. Summary

What is Tropic Movement?

Tropic movement or tropism is a directional movement shown by a plant as a response to an external stimulus. Thus, the tropic movement depends on the direction of the stimulus. Positive tropism is the movement towards the stimulus, while negative tropism is the movement away from the stimulus. There are different types of tropic movements such as phototropism, geotropism, hydrotropism, thigmotropism, chemotropism, etc.

Phototropism is the tropic movement as a response to sunlight while geotropism is the tropic movements as a response to gravity. Likewise, the stimulus differs between different types of tropism. However, tropic movement is a slow response compared to nastic movement. Moreover, tropism is a result of cell division.

What is Nastic Movement?

Nastic movement is a non-directional response shown by plants to an external stimulus. Most importantly, it is an immediate response of plants. Nastic movements do not depend on the direction of the stimulus. Similar to tropism, nastic movements are also vital for plants. For example, closing of the carnivorous Venus Flytrap leaf when it captures a prey is an important nastic movement. Moreover, the folding of Mimosa leaves when it receives a touch is another common nastic movement.

These movements can be mainly due to the changes in turgor pressure of the plants. Epinasty, hyponasty, photonasty, nyctinasty, chemonasty, hydronasty, thermonasty, geonasty and thigmonasty are types of nastic movements.

What are the Similarities Between Tropic and Nastic Movement?

• Tropic and nastic movements are two types of responses shown by plants.
• Both movements occur as a response to a stimulus. Hence, they are induced movements.
• Also, they are very important movements of the plants in order to grow and survive.

What is the Difference Between Tropic and Nastic Movement?

Tropic and nastic movements are two types of plant responses to external stimuli. And, the key difference between tropic and nastic movement is the direction of the response. Tropic movement is a directional response while nastic movement is a non-directional movement. Moreover, tropic movement depends on the direction of the stimulus, while nastic movement does not depend on the direction of a stimulus.

Generally, tropic movement occurs as a result of cell division while the nastic movement occurs as a result of turgor pressure. Hence, this is another difference between tropic and nastic movement.

The below info-graphic presents more facts regarding the difference between tropic and nastic movement comparatively.

Summary – Tropic vs Nastic Movement

Tropic and nastic movement are two types of induced movements plants show. Both are vital movements. But, the key difference between tropic and nastic movement is the direction of the response. Tropic movement is a directional response while nastic movement is a non-directional response to a stimulus. Thus, tropic movement depends on the direction of the stimulus while nastic movement does not.  Furthermore, tropic movement is a slow response while nastic movement is a fast response. Moreover, tropic movement occurs due to cell division while nastic movement occurs due to the changes in turgor.

Reference:

1.“Nastic Movements.” Wikipedia, Wikimedia Foundation, 21 Apr. 2019, Available here.
2. “Tropism.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 7 Apr. 2009, Available here.

Image Courtesy:

1. “Phototropism” By Tangopaso – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Mimosa Pudica” By Hrushikesh – Own work, CC0) via Commons Wikimedia